The invention relates to a particle beam apparatus comprising a vacuum chamber which is provided with an aperture that can be closed and which can be evacuated by heating.
Such an apparatus in the form of an electron beam apparatus is known from WO 88/080. The apparatus described therein includes a field emission source which is accommodated in a chamber which can be evacuated to a pressure of, for example 10.sup.-9 torr. Via an aperture which can be closed by means of a valve, the chamber communicates with a further apparatus chamber which is also to be evacuated, for example a working space for the electron beam. In such a space such a high vacuum is usually difficult to achieve. During a first phase of the evacuation of the high vacuum chamber the valve is open and during a further phase it is closed. The final evacuation process can be realized, for example by a getter. Opening and closing of the valve is coupled to controlled displacement of a support for the electron emitter, leading to the open and closed state of the valve. Such valve control is comparatively complex, is dependent on another member to be displaced, and can readily give rise to an undesirable state so that either evacuation is not effective or the vacuum in the high vacuum chamber is lost at an undesirable instant.